Is there a commas-in-between idiom?

[Ernesto García García]

Hi experts,

it's very common that I have a list and I want to print it with commas
in between. How do I do this in an easy manner, whithout having the
annoying comma in the end?

<code>

list = [1,2,3,4,5,6]

# the easy way
for element in list:
print element, ',',

print
# this is what I really want. is there some way better?
if (len(list) 0):
print list[0],
for element in list[1:]:
print ',', element,

</code>

Thx,
Ernesto

[Christian Joergensen]

Ernesto García García <ti**********************@gmail.comwrites:

Hi experts,

it's very common that I have a list and I want to print it with commas
in between. How do I do this in an easy manner, whithout having the
annoying comma in the end?

>>list = [1,2,3,4,5,6]
print ','.join(map(str, list))

1,2,3,4,5,6

--
Christian Joergensen | Linux, programming or web consultancy
http://www.razor.dk | Visit us at: http://www.gmta.info

[Peter Otten]

Ernesto García García wrote:

it's very common that I have a list and I want to print it with commas
in between. How do I do this in an easy manner, whithout having the
annoying comma in the end?

>>items = [1, 2, 3, "many"]
print ", ".join(str(item) for item in items)

1, 2, 3, many

Peter

[James Stroud]

Ernesto García García wrote:

Hi experts,

it's very common that I have a list and I want to print it with commas
in between. How do I do this in an easy manner, whithout having the
annoying comma in the end?

<code>

list = [1,2,3,4,5,6]

# the easy way
for element in list:
print element, ',',

print
# this is what I really want. is there some way better?
if (len(list) 0):
print list[0],
for element in list[1:]:
print ',', element,

</code>

Thx,
Ernesto

print ",".joint(some_list)

Where what you have named "list" is now called "some_list" because it is
terribly ill-advised to reassign the name of a built-in type.

James

[Ernesto García García]

Ernesto García García wrote:

Hi experts,

it's very common that I have a list and I want to print it with commas
in between. How do I do this in an easy manner, whithout having the
annoying comma in the end?

<code>

list = [1,2,3,4,5,6]

# the easy way
for element in list:
print element, ',',

print
# this is what I really want. is there some way better?
if (len(list) 0):
print list[0],
for element in list[1:]:
print ',', element,

</code>

Thx,
Ernesto

mylist = [1,2,3,4,5,6]
print ','.join(map(str, mylist))

Great solution!

Thank all of you,
Ernesto

[Tim Peters]

]Ernesto García García]

it's very common that I have a list and I want to print it with commas
in between. How do I do this in an easy manner, whithout having the
annoying comma in the end?

<code>

list = [1,2,3,4,5,6]

# the easy way
for element in list:
print element, ',',

print
# this is what I really want. is there some way better?
if (len(list) 0):

More idiomatic as

if len(list) 0:

and even more so as plain

if list:

print list[0],
for element in list[1:]:
print ',', element,

Do you really want a space before and after each inter-element comma?

</code>

An often-overlooked alternative to playing with ",".join() is:

print str(list)[1:-1]

That is, ask Python to change the list into a big string, and just
strip the brackets off each end:

>>alist = ['a, bc', 4, True]
print str(alist)[1:-1]

'a, bc', 4, True

Note the quotes around the string element! This differs from what
your code snippet above would produce (in addition to differing wrt
spaces around inter-element commas):

a, bc , 4 , True

[Ernesto García García]

Tim Peters wrote:

More idiomatic as

if len(list) 0:

and even more so as plain

if list:

> print list[0],
for element in list[1:]:
print ',', element,

Do you really want a space before and after each inter-element comma?

No, but it was only an example. I usually go for string concatenation.

An often-overlooked alternative to playing with ",".join() is:

print str(list)[1:-1]

That's funny! Not that I like it more that the join solution, but funny
nevertheless.

Thank you,
Ernesto

[Fredrik Lundh]

Ernesto García García wrote:

it's very common that I have a list and I want to print it with commas
in between. How do I do this in an easy manner, whithout having the
annoying comma in the end?

I've collected a bunch of list pydioms and other notes here:

http://effbot.org/zone/python-list.htm

For formatting issues, see:

http://effbot.org/zone/python-list.htm#printing

</F>

[Ernesto García García]

I've collected a bunch of list pydioms and other notes here:

>
http://effbot.org/zone/python-list.htm

Thank you for the suggestion.

Ernesto

[Peter van Kampen]

On 2006-11-06, Fredrik Lundh <fr*****@pythonware.comwrote:

I've collected a bunch of list pydioms and other notes here:

http://effbot.org/zone/python-list.htm

"""
A = B = [] # both names will point to the same list
"""

I've been bitten by this once or twice in the past, but I have always
wondered what it was useful for? Can anybody enlighten me?

TIA,

PterK

--
Peter van Kampen
pterk -- at -- datatailors.com

[Georg Brandl]

Peter van Kampen schrieb:

On 2006-11-06, Fredrik Lundh <fr*****@pythonware.comwrote:

>I've collected a bunch of list pydioms and other notes here:

http://effbot.org/zone/python-list.htm

"""
A = B = [] # both names will point to the same list
"""

I've been bitten by this once or twice in the past, but I have always
wondered what it was useful for? Can anybody enlighten me?

Do you never have a situation where you want to assign the same value
to two variables?

Or are you objecting to the fact that both names point to the same object?
It couldn't be otherwise. Consider:

X = []
A = B = X

What should this do? Copy "X" and assign one copy to A, one to B?

Georg

[Gabriel Genellina]

At Wednesday 8/11/2006 16:51, Peter van Kampen wrote:

>"""
A = B = [] # both names will point to the same list
"""

I've been bitten by this once or twice in the past, but I have always
wondered what it was useful for? Can anybody enlighten me?

As an optimization, inside a method, you can bind an instance
attribute and a local name to the same object:

def some_action(self):
self.items = items = []
// following many references to self.items,
// but using items instead.

Names in the local namespace are resolved at compile time, so using
items is a lot faster than looking for "items" inside self's
namespace each time it's used.
--
Gabriel Genellina
Softlab SRL

__________________________________________________
Correo Yahoo!
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[Magnus Lycka]

Ernesto García García wrote:

list = [1,2,3,4,5,6]

Just a nit-pick: It's considered an anti-idiom
to hide builtins just as list by using it as a
name for a variable.

>>list=[1,2,3,4,5]
tuple = (1,2,3,4,5)
if list == list(tuple): print "equal"

....
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: 'list' object is not callable

>>#ouch!

....

>>l=list
del list
if l == list(tuple): print "equal"

....
equal

>>if tuple(l)==tuple: print "equal"

....
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: 'tuple' object is not callable

>>t=tuple
del tuple
if tuple(l)==t: print "equal"

....
equal

[Peter van Kampen]

On 2006-11-08, Georg Brandl <g.*************@gmx.netwrote:

Peter van Kampen schrieb:

>On 2006-11-06, Fredrik Lundh <fr*****@pythonware.comwrote:

>>I've collected a bunch of list pydioms and other notes here:

http://effbot.org/zone/python-list.htm

"""
A = B = [] # both names will point to the same list
"""

I've been bitten by this once or twice in the past, but I have always
wondered what it was useful for? Can anybody enlighten me?

Do you never have a situation where you want to assign the same value
to two variables?

In the sense that I might want two empty lists or maybe 2 ints that
are initialised as 0 (zero). That's what I (incorrectly) thought A = B
= [] did.

Or are you objecting to the fact that both names point to the same
object?

I'm not objecting to anything, merely wondering when I could/should
use this idiom. There's a nice example in another response (self.items
= items = [])

It couldn't be otherwise. Consider:

X = []
A = B = X

What should this do? Copy "X" and assign one copy to A, one to B?

Ah yes, I see the error in my ways...I skipped the A = B part too
lightly.

Thanks,

PterK
--
Peter van Kampen
pterk -- at -- datatailors.com

[Peter van Kampen]

On 2006-11-08, Gabriel Genellina <ga******@yahoo.com.arwrote:

At Wednesday 8/11/2006 16:51, Peter van Kampen wrote:

>>"""
A = B = [] # both names will point to the same list
"""

I've been bitten by this once or twice in the past, but I have always
wondered what it was useful for? Can anybody enlighten me?

As an optimization, inside a method, you can bind an instance
attribute and a local name to the same object:

def some_action(self):
self.items = items = []
// following many references to self.items,
// but using items instead.

Names in the local namespace are resolved at compile time, so using
items is a lot faster than looking for "items" inside self's
namespace each time it's used.

Nice example.

Thanks,

PterK

--
Peter van Kampen
pterk -- at -- datatailors.com